The present invention relates to intraocular lenses (IOLs) for implantation in an aphakic eye where the natural lens has been removed due to damage or disease (e.g., a cataractous lens). The present invention more particularly relates to a novel IOL designed in a first aspect to be inserted through a sub-3 mm incision made in the eye, and in a second aspect includes a sharp posterior edge to inhibit unwanted growth of lens epithelial cells (hereinafter “LECs”) between the IOL and posterior capsular bag, also known as posterior capsule opacification (hereinafter “PCO”).
A common and desirable method of treating a cataract eye is to remove the clouded, natural lens and replace it with an artificial IOL in a surgical procedure known as cataract extraction. In the extracapsular extraction method, the natural lens is removed from the capsular bag while leaving the posterior part of the capsular bag (and preferably at least part of the anterior part of the capsular bag) in place within the eye. In this instance, the capsular bag remains anchored to the eye's ciliary body through the zonular fibers. In an alternate procedure known as intracapsular extraction, both the lens and capsular bag are removed in their entirety by severing the zonular fibers and replaced with an IOL which must be anchored within the eye absent the capsular bag. The intracapsular extraction method is considered less attractive as compared to the extracapsular extraction method since in the extracapsular method, the capsular bag remains attached to the eye's ciliary body and thus provides a natural centering and locating means for the IOL within the eye. The capsular bag also continues its function of providing a natural barrier between the aqueous humor at the front of the eye and the vitreous humor at the rear of the eye.
One known problem with extracapsular cataract extraction is posterior capsule opacification, or secondary cataract, where proliferation and migration of lens epithelial cells occur along the posterior capsule behind the IOL posterior surface which creates an opacification of the capsule along the optical axis. This requires subsequent surgery, such as an Er:YAG laser capsulotomy, to open the posterior capsule and thereby clear the optical axis. Undesirable complications may follow the capsulotomy. For example, since the posterior capsule provides a natural barrier between the back of the eye vitreous humor and front of the eye aqueous humor, removal of the posterior capsule allows the vitreous humor to migrate into the aqueous humor which can result in serious, sight-threatening complications. It is therefore highly desirable to prevent posterior capsule opacification in the first place and thereby obviate the need for a subsequent posterior capsulotomy.
One method for preventing PCO is to create a sharp, discontinuous bend in the posterior capsule wall which is widely recognized by those skilled in the art as an effective method for minimizing PCO. See, for example, Posterior Capsule Opacification by Nishi, Journal of Cataract & Refractive Surgery, Vol. 25, January 1999. This discontinuous bend in the posterior capsule wall can be created using an IOL having a sharp posterior edge.
Another PCO prevention method uses an LEC-targeted pharmaceutical agent. See, for example, U.S. Pat. No. 5,620,013 to Bretton entitled “Method For Destroying Residual Lens Epithelial Cells”. While this approach is logical in theory, putting such a method into clinical practice is difficult due to complications arising, for example, from the toxicity of some of the LEC inhibiting agents themselves (e.g., saporin), as well as the difficulty in ensuring a total kill of all LECs in the capsular bag. Any remaining LECs may eventually multiply and migrate over the IOL, eventually resulting in PCO despite the attempt at LEC removal at the time of surgery.
By far the most promising method for inhibiting LEC formation on the posterior surface of an IOL is by designing the IOL to have a sharp peripheral edge particularly at the posterior surface to create a discontinuous bend in the posterior capsule wall. This discontinuous bend in the posterior capsule wall has been clinically proven to inhibit the growth and migration of LECs past this bend and along the IOL surface. One of the early reports of this PCO-inhibiting effect of a planoconvex IOL may be found in Explanation of Endocapsule Posterior Chamber Lens After Spontaneous Posterior Dislocation by Nishi et al, J Cataract & Refractive Surgery—Vol 22, March 1996 at page 273 wherein the authors examined an explanated planoconvex PMMA IOL where the posterior surface of the IOL was planar and formed a square edge with the peripheral edge of the IOL:
“Macroscopic view of the explanted IOL and capsule revealed a 9.5 mm capsule diameter. The open circular loops fit well along the capsule equator. The capsule equator not in contact with the haptic was also well maintained (FIG. 3). An opaque lens mass (Soemmering's ring cataract) was seen between the haptics and optic. The posterior capsule facing the IOL optic was clear. Histopathological examination of the explanted capsule revealed few epithelial cells (LECs) on the posterior capsule. Between the loops and the optic, a lens mass with accumulation at the edge of the optic was seen (FIG. 4). There was an obvious bend in the posterior capsule at this site.” (Emphasis added.)
Thus, in the years since this report, the industry has seen much activity on creating IOLs with a sharp posterior edge so as to create a sharp, discontinuous bend in the posterior capsule wall.
Another trend in modern day cataract surgery is to reduce the corneal incision size as much as possible. This is because larger incision sizes have been attributed to unwanted post-surgical conditions such as incision-induced astigmatism, for example. IOLs and IOL injectors capable of successfully injecting the IOL through a sub 3-mm incision is desirable to most present-day cataract surgeons. Since the IOL must undergo compression and other forces as it is passed through the IOL injector and injected into the eye, the dimensions (particularly the cross-section) of the IOL must accordingly be minimized. An IOL designer is thus further challenged in making an IOL which on the one hand will have the strength and stability to remain centered in the eye, and on the other hand have small enough dimensions to pass through a sub-3 mm injector and into the eye. It will be appreciated that these are often competing design goals in that reducing IOL dimensions to fit through a smaller incision can result in a decrease in the strength and stability of the IOL in the eye. The strength and stability of the IOL within the eye is of course crucial in obtaining and maintaining the intended vision correction afforded by the IOL. Thus, an IOL designer cannot reduce IOL dimensions without first understanding and then compensating, through careful design, the effect such downsizing in dimensions has on the strength and stability of the IOL.
There therefore remains a need for an improved IOL design and method which addresses the problem of LEC migration and subsequent PCO formation, is dimensioned to fit through a sub-3 mm injector, and is strong and stable enough to remain properly positioned in an eye.